The invention relates to a flame monitor for an oil- or gas-operated burner.
German Patent DE 197 46 786 C2 discloses a flame monitor for blue-burning flames of an oil or gas burner, in which use is made of a semiconductor detector with a spectral sensitivity in the near ultraviolet with an evaluation circuit connected downstream, which influences a regulator for the fuel/combustion air ratio in accordance with the spectral distribution of the flame radiation. However, when the flame radiation shifts toward longer wavelengths, the xe2x80x9cyellow regionxe2x80x9d, this can lead to problems such that, despite the proportion of combustion air being increased, the shift increases and the fuel supply is thereupon switched off. Evaluation of the radiation received by the photosensor with regard to whether the burner is burning or, in the case where it is not burning, the fuel supply is to be switched off as far as possible immediately, is not provided in this case.
German Patent DE 198 09 653 C1 discloses a flame monitor for blue-burning flames of an oil or gas burner, which has a photosensor which detects the flame radiation and whose sensitivity rises sharply from ultraviolet to infrared, and comprises an evaluation circuit which is connected downstream and switches off the fuel supply if the radiation falls within the range from 200 to 500 nm or the increase in the detected radiation intensity above 500 nm indicates movement out of the blue region. In this case, the signal of the photosensor is evaluated in a two-channel manner, one relating to ultraviolet radiation up to 500 nm and the other relating to visible and infrared radiation. A special photosensor with special evaluation is required in this case.
It is an object of the invention to provide a flame monitor which enables identification of whether the burner is burning, i.e. a flame is present, in a very simple manner.
According to the invention there is provided a flame monitor for an oil- or gas-operated burner, having a photosensor which detects the optical flame radiation and the pulsation thereof, and having an evaluation circuit which is connected downstream of said photosensor and ascertains whether the radiation received by the photosensor corresponds to that of a burning flame and, in the event of a negative result, generates a switch-off signal for the fuel supply,
wherein the evaluation circuit determines the number of zero crossings of the processed signal of the photosensor within a predetermined unit of time and compares it with a predetermined limit value, a switch-off signal for the fuel supply being generated when said limit value is undershot, the signal of the photosensor, freed from the DC voltage component and noise, being processed by corresponding amplification to form square-wave pulses.
Further objects, advantages and embodiments of the invention will become apparent from the following description and the claims.